Where light is propagated between two light-propagating media of different refractive indices, since there is transmission and reflection of light at the interface, it is typically difficult to transfer, with a high efficiency, light from one light-propagating medium to the other light-propagating medium and maintain this state. A conventional grating coupling method shown in Non-Patent Document No. 1, for example, can be mentioned as a technique for taking light into a transparent sheet from an environmental medium such as the air. FIGS. 32(a) and 32(b) are diagrams illustrating the principle of the grating coupling method, showing a cross-sectional view and a plan view of a light-transmitting layer 20 with a linear grating of a pitch Λ provided on a surface thereof. As shown in FIG. 32(a), if light 23a of a wavelength λ is allowed to enter the grating at a particular angle of incidence θ, it can be coupled to guided light 23B propagating through the light-transmitting layer 20.